Adding data to an array

I am trying a add data to an array using a while loop but it seems to be adding the data as a string not array. Loops/arrays are something I'm still learning any help would be great.

$c = 0;
$numberofcustom = 5;
$defaults = array(
'title' => __('Follow Us!', 'smw'),
 'text' => ''
);
while ($c < $numberofcustom) {
    $customnumber = $c + 1;
    $defaults.=array(
        'custom' . $customnumber . 'name' => __('', 'smw'),
        'custom' . $customnumber . 'icon' => __('', 'smw'),
        'custom' . $customnumber . 'url' => __('', 'smw')
    );
    $c++;
}

print_r($defaults);

The problem seems to be with adding the data from the loop if I do a print_r just on that I just get "array" back.

Any help would be appreciated.

UPDATE

I decided I don't need a multi dimensional array so I used the suggestions below and came up with

while( $c < $numberofcustom){
    $customnumber = $c+1;
        $defaults['custom'.$customnumber.'name'] = __('', 'smw');
        $defaults['custom'.$customnumber.'icon'] = __('', 'smw');
        $defaults['custom'.$customnumber.'url'] = __('', 'smw');
    $c++;       
    }

Copyright Notice：Content Author:「Brooke.」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/7460356/adding-data-to-an-array